1. Field of the Invention
The present invention relates to an exposure apparatus and a method of manufacturing an article.
2. Description of the Related Art
An exposure apparatus which projects and transfers a pattern formed on an original onto a substrate by a projection optical system is employed to manufacture an article such as a microdevice using the photolithography technique. The resolution of an image to be projected depends on the wavelength of exposure light, and the numerical aperture (HA) of the projection optical system, so the shorter the wavelength, and the larger the numerical aperture, the higher the obtained resolution becomes.
As a demand for miniaturizing formed elements has arisen, the wavelength of exposure light has shortened. More specifically, the wavelength of exposure light is shorter in the order of an ultra-high pressure mercury lamp (i-line (wavelength: about 365 nm)), a KrF excimer laser (wavelength: about 248 nm), and an ArF excimer laser (wavelength: about 193 nm). However, the photolithography technique which uses ultraviolet exposure light cannot cope with further miniaturization. Hence, to transfer a pattern as very fine as 0.1 μm or less at a high resolution, an exposure apparatus which uses EUV (Extreme Ultraviolet) light with a wavelength of about 5 nm to 15 nm shorter than that of ultraviolet light has been developed. Such an exposure apparatus is called an EUV exposure apparatus. An optical system of the EUV exposure apparatus is formed by a plurality of optical members (total reflection mirrors). In the EUV exposure apparatus, the requirement for the stability (positioning reproducibility) of the position and attitude of each optical member is very high to project a pattern at a high resolution.
Japanese Patent Laid-Open No. 2006-66836 describes a supporting structure for an optical member. The optical member has a flange portion on its periphery. A ball press ring which supports the optical member includes an annular frame member, three supporting portions arranged on one surface of the frame member to have an angular pitch of 120°, and a parallel-plate spring which connects the frame member and supporting member to each other. The optical member is fixed to the supporting member by adhering a bridge member to the side surface of its flange portion and that of the supporting member by an adhesive agent while the flange portion is disposed on the supporting member.
In a configuration in which the optical member is fixed by the adhesive agent, a problem resulting from generation of a gas from the adhesive agent is posed. Such a gas is called outgas. In, for example, an EUV exposure apparatus, outgas may become a factor which absorbs EUV light from a light source. Also, outgas may adhere to the surface of the optical member to form a film, or form a reaction product with other substances and adhere to the surface of the optical member. This may become a factor which shortens the life of the optical member.